In hot rolling, it is requested to obtain desired material characteristics of a product, such as tensile strength, and to keep surface quality of the product excellent. In order to respond to these requests, a temperature managing position is set on an outlet side of a rolling mill, and temperature control is performed for making a material temperature at the temperature managing position coincide with a designated target value over an entire length of a material.
As means for adjusting the material temperature in hot rolling, next three ones have been known. Conventionally, various temperature control methods using the three temperature adjusting means have been proposed.
First temperature adjusting means: Changing rolling speed
Second temperature adjusting means: Changing cooling water flow rate of cooling device
Third temperature adjusting means: Changing electric power of induction heating device
For example, a temperature control method utilizing the first and the second temperature adjusting means is shown in Patent Literature 1. According to the method disclosed in Patent Literature 1, a cooling water flow rate to be needed is calculated using a temperature model regarding a number of calculation points of a material in a longitudinal direction, and the cooling water flow rate is operated by feedforward control. In addition, the cooling water flow rate is operated by feedback control so that a deviation between a material temperature and a target value in a temperature managing position is reduced. Further, when the cooling water flow rate reaches an upper limit or a lower limit, a rolling speed is corrected by the feedback control so that the material temperature becomes the target value.
In addition, a temperature control method utilizing the third temperature adjusting means is shown in Patent Literature 2. In raising a temperature of a material in a heating furnace, when the material comes into contact with a water-cooled support beam in the furnace, a skid mark due to decrease in temperature is generated at a portion of the material having come into contact with the support beam. According to the method disclosed in Patent Literature 2, fluctuations in temperature in a temperature managing position is suppressed by increasing electric power of induction heating locally with respect to the skid mark.